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Y. Ruiz et al.
Figure 21.4a shows the multivariate analysis of principal components (PCA),
with mutagenic species of PAHs, penta- and hexa-chlorinated congeners, Cd, Zn
and neoplastic prevalence as variables, and the samplings as trials. The data matrix
consisted of 180 elements (5 variables 36 samples). The number of factors
extracted from the variables was determined according to Kaiser’s rule, which only
retains factors with eigenvalues that exceed one. Most of the variance (87.5 %)
was explained by the first two main components: PC1 explained 61.1 % of the
total variance and PC2 accounted for 26.4 %. Three other factors were extracted
as PC3, PC4 and PC5 which accounted for 9.9, 1.8 and 0.8 % of the total variance,
respectively. PC1 was characterized by a high influence of neoplasia (r < 0.91),
whereas PC2 was characterized by high correlation with Zn and PAHs (r < 0.78
and r > 0.59, respectively). PC3 was also corelated with Zn and PAHs (r > 0.57 and
r > 0.68, respectively), PC4 by PCBs (r < 0.94) and PC5 by Cd (r > 0.99).
The score plot of the first two components allows the characterization of the
samples. This plot shows how the samples are inter-related depending on the
variables chosen. In this context, the distances between the samples were measured
by multivariate cluster analysis (Fig. 21.4b), which can be overlapped to PCA
analysis. The resulting cluster identified three main groups of samples. The first
group corresponded to samples without neoplasia and minimal concentrations of
pollutants. The second group included samples with high neoplasia prevalence (6.7–
63.4 %), medium levels of PAHs and high levels of PCBs and metals. Finally, the
third group corresponded to samples with maximum levels of PAHs, PCBs and
metals, but low neoplasia prevalence (6.7–10%), suggesting a lethal effect.
Discussion
There are few references to gonadal neoplasms in bivalve molluscs. Most report
effects on the germinal cells (germinoma), but in some cases both germinal cells
and connective tissue cells (gonadoblastoma) (Pauley and Sayce 1968; Peters et al.
1994). These pathologies have been related to age, size, sex, season and reproductive
cycle, and usually have a negative impact on reproduction (Yevich and Barszcz
1976; Hesselman et al. 1988; Bert et al. 1993; Peters et al. 1994; Ford et al. 1997;
Alonso et al. 2001; Darriba et al. 2006).
Similar neoplastic alterations to those described as germinoma by Alonso et al.
(2001) were observed in this work. Initially, the proliferation of germinal neoplastic
cells within gonadal follicles suggests a tumor in situ. However, breaking of
follicular membrane and invasion of the connective tissue by neoplastic cells
demonstrates its infiltrating capacity. The presence of karyorrhexis, karyolysis and
cytoplasm vacuolization of neoplastic cells are also indicative of necrotic processes.
All these anomalies support the diagnosis of a germinoma in Stage 3, according to
Bert et al. (1993) and Barber (2004).
Proliferation of haemocytes and phagocytes in tumor areas can be considered
as a defensive response of organisms. Frequently, phagocytes contain degradation
Y. Ruiz et al.
Figure 21.4a shows the multivariate analysis of principal components (PCA),
with mutagenic species of PAHs, penta- and hexa-chlorinated congeners, Cd, Zn
and neoplastic prevalence as variables, and the samplings as trials. The data matrix
consisted of 180 elements (5 variables 36 samples). The number of factors
extracted from the variables was determined according to Kaiser’s rule, which only
retains factors with eigenvalues that exceed one. Most of the variance (87.5 %)
was explained by the first two main components: PC1 explained 61.1 % of the
total variance and PC2 accounted for 26.4 %. Three other factors were extracted
as PC3, PC4 and PC5 which accounted for 9.9, 1.8 and 0.8 % of the total variance,
respectively. PC1 was characterized by a high influence of neoplasia (r < 0.91),
whereas PC2 was characterized by high correlation with Zn and PAHs (r < 0.78
and r > 0.59, respectively). PC3 was also corelated with Zn and PAHs (r > 0.57 and
r > 0.68, respectively), PC4 by PCBs (r < 0.94) and PC5 by Cd (r > 0.99).
The score plot of the first two components allows the characterization of the
samples. This plot shows how the samples are inter-related depending on the
variables chosen. In this context, the distances between the samples were measured
by multivariate cluster analysis (Fig. 21.4b), which can be overlapped to PCA
analysis. The resulting cluster identified three main groups of samples. The first
group corresponded to samples without neoplasia and minimal concentrations of
pollutants. The second group included samples with high neoplasia prevalence (6.7–
63.4 %), medium levels of PAHs and high levels of PCBs and metals. Finally, the
third group corresponded to samples with maximum levels of PAHs, PCBs and
metals, but low neoplasia prevalence (6.7–10%), suggesting a lethal effect.
Discussion
There are few references to gonadal neoplasms in bivalve molluscs. Most report
effects on the germinal cells (germinoma), but in some cases both germinal cells
and connective tissue cells (gonadoblastoma) (Pauley and Sayce 1968; Peters et al.
1994). These pathologies have been related to age, size, sex, season and reproductive
cycle, and usually have a negative impact on reproduction (Yevich and Barszcz
1976; Hesselman et al. 1988; Bert et al. 1993; Peters et al. 1994; Ford et al. 1997;
Alonso et al. 2001; Darriba et al. 2006).
Similar neoplastic alterations to those described as germinoma by Alonso et al.
(2001) were observed in this work. Initially, the proliferation of germinal neoplastic
cells within gonadal follicles suggests a tumor in situ. However, breaking of
follicular membrane and invasion of the connective tissue by neoplastic cells
demonstrates its infiltrating capacity. The presence of karyorrhexis, karyolysis and
cytoplasm vacuolization of neoplastic cells are also indicative of necrotic processes.
All these anomalies support the diagnosis of a germinoma in Stage 3, according to
Bert et al. (1993) and Barber (2004).
Proliferation of haemocytes and phagocytes in tumor areas can be considered
as a defensive response of organisms. Frequently, phagocytes contain degradation